Explorer's Handbook (Eberron supplement)
Cataclysm Mage [+1]
Logical Entry: Wizard 5 (many of its abilities are actually tied to Intelligence, not Charisma. This makes Sorcerer a much worse choice)
Reasoning: Very easy to qualify with DM cooperation or just a clever backstory ("must have had a vision"). 9/10 Spellcasting progression and you gain some odd AoE-damage dealing abilities and some odd bonuses, but the capstone ability: Choose any dragonmark from lesser to greater, which you may change each day. Catch? The dragons WILL kill you (it's not even a part of "CM in the world", it's a part of the ability that makes Eberron dragons want to kill you. Bad) when they know that you have this dragonmark-for-free abiliy.
For those of you who aren't familiar with dragonmarks, it translates roughly to: true seeing, find the path, animal growth, SNA V, heal, heroes' feast, mage's magnificent mansion, fabricate, major creation, overland flight, teleport, sending, globe of invulnerability, mislead, prying eyes, shadow walk, control winds, control weather, mage's faithful hound, greater glyph of warding OR guards and wards once per day. And that's just Greater Dragonmarks, and you can even take the Mark of Death, which requires much DM cooperation (can make someone a Lich upon death, if the legends are correct).
Any one of them, plus various bonuses and destructive abilities based on Intelligence (unlike many other PrCs with similar abilities) makes it a very potent wizard, especially if you are an Eberron person.
The catch (yet again): You must fulfill "personal prophecies" laid out in the class description to advance in the class. This includes easy tasks such as "Be swallowed whole" and "Die", but also more cryptic adventures such as "speak with a giant who never dreams" etc etc (total of 12). Therefore, unless your DM and fellow players are willing to cooperate (or unless you start at ECL 15 or higher), you may have some problems there.
Overall, a very, very nice class whose capstone ability gives you a virtual 6th-level or lower spell slot with predetermined spell-like abilities in them. Be careful around dragons though. They'll hate you for taking that capstone ability.
Also: this class (if it advances infusions) can enable you to make a Warforged Artificer 7/CM 10/Cannith Wand Adept 3, because you'll meet the dragonmark requirement of CWA then.
Thunder Guide [-1]
Logical Entry: Fighter 4, Barbarian 4, Ranger 4, Rogue 6 and so on. Not that hard to qualify, not that much to gain either.
Reasoning: 3/4 BAB and good Fort. Lets you gain some negligible bonuses based on your choices of "Thunder lore" and "Native ties" abilities, and the capstone ability makes you famous. Really! The capstone ability lets you use the title of "Lord" (or "Lady") in any of the Four Nations (r.i.p. Cyre), and lets you use transports for free. You're so famous that those "companies" (dragonmarked houses) benefit from just the fact that you were onboard with their transport. That's the capstone ability of the class.
If you haven't quite grasped the gist of it, the one before that (9th-level) gives you money. 1,000gp per point of Charisma you have, and that's the brand loyalty to write your stories in the most popular newspaper in the whole continent. Everyone in the world will know and love the over-the-top descriptions of your daring adventures.
So if you want to play a class that's actually based on gaining fame and fortune as its class ability, it's the class for you. CO perspective? Not so hot. Unless you want to play a guy called Guybrush Threepwood, because you can hold your breath for 1 minute per point of Constitution. Yes, you can hold your breath for ten minutes.
Windwright Captain [-2]
Logical Entry: Half-elf bard 7, artificer 7
Reasoning: 3/5 spellcasting progression (specifically advances infusion) that lets you control your own airship like it's your own body. I mean, really. You have to pay up to 9k XP to actually access the abilities that makes this class unique. So unless you're going to name your own airship Millenium Falcon and be a super-pilot, stay well away from the class.
2 levels of the class might be worth it if you want to borrow an airship indefinitely though. I'd just spend 92k and forget about it myself.